Conventionally, an olefin-based hollow filament or a hollow filament obtained using an ion-exchange fluororesin is used to humidify the gas fed to a fuel electrode or an air electrode of a fuel cell. However, hollow filaments have high ventilation resistance and make it difficult to raise the flow rate. Therefore, a membrane-type moistening module using a vapor-permeable membrane shows promise.
A composite membrane 10 having a moisture-permeable resin layer 30 on both surfaces of a porous polymeric resin article 20 is disclosed, for example, in Patent Document 1 as a vapor-permeable membrane, as shown in FIG. 1. However, in many cases, the composite membrane 10 cannot exhibit sufficient moisture permeability with one membrane. Therefore, as shown in FIG. 2, a plurality of composite membranes 10 is superposed while open spaces are left that can serve as gas channels. Also, spacers 50 are inserted between the composite membranes 10 in order to form the open spaces. When the moisture-permeable resin layers 30 are exposed on the surface of the composite membranes 10, the moisture-permeable resin layers 30 are damaged by the spacers 50. Furthermore, when exposed to hot water over a long period of time, the moisture-permeable resin layers 30 have inadequate durability. The adhesive strength between the composite membranes 10 and the spacers 50 is also low.
Patent Document 2 discloses a composite membrane 10 in which, in a layered object composed of a porous membrane 20 and a reinforcing element (nonwoven fabric or the like) 40, a moisture-permeable resin layer 30 is interposed between the reinforcing element 40 and the porous membrane 20 along the border that faces the membrane, as shown in FIG. 3. The risk that the moisture-permeable resin layer 30 will be damaged by the spacer 50 decreases since the moisture-permeable resin layer 30 is protected with the reinforcing element 40 and the porous membrane 20. Patent Document 3 will be described below.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2006-160966.    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2006-150323.    [Patent Document 3] U.S. Pat. No. 5,418,054.
However, according to a study conducted by the inventors, bringing both the gas barrier properties and moisture permeability to a higher level was difficult to achieve in the composite membrane (vapor-permeable membrane) 10 disclosed in Patent Document 2. For example, in the composite membrane 10 disclosed in Patent Document 2, the moisture permeability deteriorates when the gas barrier properties are raised, and the gas barrier properties deteriorate when the moisture permeability is raised.
The present invention relates to a composite membrane capable of selectively transmitting water included in gas and liquid; preferably relates to a composite membrane that can be used as a dehumidification membrane, moistening membrane, pervaporation membrane (for example, a membrane for separating water and other liquids (such ethanol and other alcohols)); and more preferably relates to a composite membrane that can be used as a separation membrane to selectively transmit water vapor from a hot and humid gas (for example, a moistening membrane for using the water vapor included in the effluent gas (especially effluent gas on the side of an air electrode) of a fuel cell electrode in the humidification of the gas fed to a fuel electrode or the air electrode (especially the fuel electrode)).
However, according to a study conducted by the inventors, bringing both the gas barrier properties and moisture permeability to a higher level was difficult to achieve in the composite membrane (vapor-permeable membrane) 10 disclosed in Patent Document 2. For example, in the composite membrane 10 disclosed in Patent Document 2, the moisture permeability deteriorates when the gas barrier properties are raised, and the gas barrier properties deteriorate when the moisture permeability is raised.
The present invention was developed with a focus on circumstances such as those described above, and an object thereof is to provide a composite membrane 10 in which the balance between the gas barrier properties and moisture permeability is further improved; and to provide a moisture adjustment module using the composite membrane 10.
Another object of the present invention is to provide a composite membrane 10 further having excellent scratch resistance when brought into contact with a spacer or another external object 50; and to provide a moisture adjustment module using the composite membrane.
Yet another object of the present invention is to provide a composite membrane 10 further having excellent adhesive properties in relation to an extern object (spacer) 50; and to provide a moisture adjustment module using the composite membrane.
Yet another object of the present invention is to provide a less expensive composite membrane 10 that provides very high moisture vapor transport rates, very low air permeability and excellent long-term durability while simultaneously utilizing reduced quantities of a relatively expensive fluoropolymer resin; and a moisture adjustment module using the composite membrane.
The present invention was developed with a focus on circumstances such as those described above, and an object thereof is to provide a composite membrane 10 in which the balance between the gas barrier properties and moisture permeability is further improved; and to provide a moisture adjustment module using the composite membrane 10.
Another object of the present invention is to provide a composite membrane 10 further having excellent scratch resistance when brought into contact with a spacer or another external object 50; and to provide a moisture adjustment module using the composite membrane.
Yet another object of the present invention is to provide a composite membrane 10 further having excellent adhesive properties in relation to an external object (spacer) 50; and to provide a moisture adjustment module using the composite membrane.
Yet another object of the present invention is to provide a less expensive composite membrane 10 that provides very high moisture vapor transport rates, very low air permeability and excellent long-term durability while simultaneously utilizing reduced quantities of a relatively expensive fluoropolymer resin; and a moisture adjustment module using the composite membrane.